'Raster Shaders' on Commodore 64

Video cards can execute small programs whenever a pixel is displayed on screen.
Commodore 64 can execute small programs whenever a raster line is displayed on TV.

Pixel shaders can be used to create realistic lighting, special effects and even compute physics!
‘Raster shaders’ can be used to split screen, display more sprites and even play sound!

Transcript

1. “Raster Shaders” on
2. I keep old computers alive mehowte  Michał Taszycki on
3. I’m making a weekly video course about programming Commodore 64 h/p:/ /64bites.com/
4. Commodore 64 belongs to the past…
5. Today
6. Back then
7. Today
8. Back then
9. Back then
10. Back then?
11. Today!
12. Pixel Shader varying vec3 N; varying vec3 v; void main(void) { vec3 L = normalize(gl_LightSource[0].position.xyz - v); vec4 Idiff = gl_FrontLightProduct[0].diffuse * max(dot(N,L), 0.0); Idiff = clamp(Idiff, 0.0, 1.0); gl_FragColor = Idiff; }
13. “Raster Shader” irq: lda #$ff sta $d019 ldx #$05 d: dex bne d ldx #$00 c: ldy #$08 a: lda colors,x sta $d020 sta $d021 inx dey beq c txa ldx #$07 b: dex bne b tax cpx #$8c bcc a
14. Enough talking!
15. Let’s code!
16. A minimal program :BasicUpstart2(main) main: rts
18. LDA adress LDA #value RAM ➞ A register STA address A register ➞ RAM Most important instructions
19. rts main: lda # sta background_color lda # sta border_color GRAY DARK_GRAY Border & Backgound Colors .label border_color = $d020 .label background_color = $d021 :BasicUpstart2(main)
20. Macros rts main: lda # sta background_color lda # sta border_color GRAY DARK_GRAY
21. rts main: lda # sta background_color lda # sta border_color GRAY DARK_GRAY .macro background(color) { } Macros
22. lda # sta background_color rts main: :background( ) color lda # sta border_color GRAY DARK_GRAY .macro background(color) { } Macros
23. lda # sta background_color rts main: :background( ) color lda # sta border_color GRAY DARK_GRAY .macro background(color) { } Macros
24. lda # sta background_color rts main: .macro border(color) { } :background( ) color lda # sta border_color GRAY DARK_GRAY .macro background(color) { } Macros
25. :border( ) .macro background(color) { } lda # sta background_color rts main: .macro border(color) { } :background( ) color lda # sta border_color GRAY DARK_GRAY color Macros
27. Raster Bar // long delay :background(BLACK) :background(DARK_GRAY)
28. Delay :background(BLACK) :background(DARK_GRAY) nop
29. :background(BLACK) :background(DARK_GRAY) nop nop Delay
30. :background(BLACK) :background(DARK_GRAY) nop nop nop Delay
31. :background(BLACK) :background(DARK_GRAY) nop // ... many more nops nop nop Delay
32. :background(BLACK) :background(DARK_GRAY) .for (var i = 0; i < ; i++) { nop } 230 Delay
33. .macro nops( ) { } .for (var i = 0; i < ; i++) { nop } :background(BLACK) :background(DARK_GRAY) 230 count Delay
34. :nops( ) .macro nops( ) { } .for (var i = 0; i < ; i++) { nop } :background(BLACK) :background(DARK_GRAY) 230 count count Delay
35. Interrupts raster_bars_irq: jmp irq_handler :nops( ) :background(BLACK) :background(DARK_GRAY) 230
36. // Disable IRQ handling sei // inject the handler lda #<raster_bars_irq sta irq_vector lda #>raster_bars_irq sta irq_vector + 1 // Enable IRQ handling cli Interrupts
38. // inject the handler lda #<raster_bars_irq sta irq_vector lda #>raster_bars_irq sta irq_vector + 1 Let’s Disable Timer cli sei
39. cli sei Let’s Disable Timer
40. cli sei // Disable the interrupt generated by timers lda #%01111111 sta cia1_interrupt_control_register sta cia2_interrupt_control_register // Negate already scheduled interrupts lda cia1_interrupt_control_register lda cia2_interrupt_control_register Let’s Disable Timer
41. Let’s Enable Raster cli sei // Disable the interrupt generated by timers lda #%01111111 sta cia1_interrupt_control_register sta cia2_interrupt_control_register // Negate already scheduled interrupts lda cia1_interrupt_control_register lda cia2_interrupt_control_register // Enable raster interrupts lda #%00000001 sta vic2_interrupt_control_register
42. Choose Raster Line cli sei // Disable the interrupt generated by timers lda #%01111111 sta cia1_interrupt_control_register sta cia2_interrupt_control_register // Negate already scheduled interrupts lda cia1_interrupt_control_register lda cia2_interrupt_control_register // Enable raster interrupts lda #%00000001 sta vic2_interrupt_control_register :request_raster_irq(106, raster_bars_irq)
43. .macro request_raster_irq(line_number, handler) { } Choose Raster Line
44. .macro request_raster_irq(line_number, handler) { } lda #<handler sta irq_vector lda #>handler sta irq_vector + 1 Choose Raster Line
45. .macro request_raster_irq(line_number, handler) { } lda #<handler sta irq_vector lda #>handler sta irq_vector + 1 lda #line_number sta vic2_rasterline_register Choose Raster Line
46. .macro request_raster_irq(line_number, handler) { } lda #<handler sta irq_vector lda #>handler sta irq_vector + 1 .if (line_number > 255) { :set_bits(screen_control_register, %10000000) } else { :clear_bits(screen_control_register, %10000000) } lda #line_number sta vic2_rasterline_register Choose Raster Line
47. .macro set_bits(address, bit_mask) { lda address ora #bit_mask sta address } .macro clear_bits(address, bit_mask) { lda address and #255 - bit_mask sta address } Choose Raster Line
48. IRQ Acknowledged? jmp irq_handler raster_bars_irq: :background(BLACK) :nops(230) :background(DARK_GRAY)
49. Przerwanie obsłużone? raster_bars_irq: :background(BLACK) :nops(230) :background(DARK_GRAY) lda #%00000001 sta vic2_interrupt_status_register jmp irq_handler
50. Przerwanie obsłużone? raster_bars_irq: :background(BLACK) :nops(230) :background(DARK_GRAY) :exit_irq_handler() .macro exit_irq_handler() { } lda #%00000001 sta vic2_interrupt_status_register jmp irq_handler
52. Stabilization :exit_irq_handler() raster_bars_irq: :nops(14) :background(BLACK) :nops(230) :background(DARK_GRAY)
54. Raster Bars! :exit_irq_handler() raster_bars_irq:
55. :nops(14) :background(BLACK) :nops(4) :background(DARK_GRAY) :nops(29) :background(GRAY) :nops(29) :background(LIGHT_GRAY) :nops(29) :background(WHITE) Raster Bars! :exit_irq_handler() raster_bars_irq:
56. :nops(14) :background(BLACK) :nops(4) :background(DARK_GRAY) :nops(29) :background(GRAY) :nops(29) :background(LIGHT_GRAY) :nops(29) :background(WHITE) Raster Bars! :exit_irq_handler() raster_bars_irq: // ...
57. :nops(14) :background(BLACK) :nops(4) :background(DARK_GRAY) :nops(29) :background(GRAY) :nops(29) :background(LIGHT_GRAY) :nops(29) :background(WHITE) Raster Bars! :exit_irq_handler() raster_bars_irq: // ... // ...
58. :nops(14) :background(BLACK) :nops(4) :background(DARK_GRAY) :nops(29) :background(GRAY) :nops(29) :background(LIGHT_GRAY) :nops(29) :background(WHITE) Raster Bars! :exit_irq_handler() raster_bars_irq: :nops(29) :background(LIGHT_GRAY) :nops(29) :background(GRAY) :nops(29) :background(DARK_GRAY) :nops(29) :background(BLACK) :nops(4) :background(DARK_GRAY) // ... // ...
60. Hardware Sprites
61. // Enable all 8 sprites lda #%11111111 sta sprites.enable_bits Hardware Sprites
62. // Enable all 8 sprites lda #%11111111 sta sprites.enable_bits .for (var i = 0; i < 8; i++) { :set_sprite_position_x(i, 60 + 32 * i) } Hardware Sprites
63. .macro set_sprite_position_x(index, position_x) { } Hardware Sprites
64. .macro set_sprite_position_x(index, position_x) { } lda #position_x sta sprites.positions + index*2 + 0 Hardware Sprites
65. .macro set_sprite_position_x(index, position_x) { } .if (position_x > 255) { :set_bits(sprites.position_x_high_bits,1<<index) } else { :clear_bits(sprites.position_x_high_bits,1<<index) } lda #position_x sta sprites.positions + index*2 + 0 Hardware Sprites
66. More Interrupts raster_bars_irq: :exit_irq_handler() // ... :nops(14)
67. sprite_row_irq1: :exit_irq_handler() // ... raster_bars_irq: :exit_irq_handler() // ... :nops(14) More Interrupts
68. sprite_row_irq1: :exit_irq_handler() // ... raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :nops(14) More Interrupts
69. sprite_row_irq1: :exit_irq_handler() // ... :request_raster_irq(106, raster_bars_irq) raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :nops(14) More Interrupts
70. sprite_row_irq1: :exit_irq_handler() // Set the y-position, bitmaps and colors :sprites_row(70, 0, 3) raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :request_raster_irq(106, raster_bars_irq) :nops(14) More Interrupts
72. sprite_row_irq1: :exit_irq_handler() // Set the y-position, bitmaps and colors :sprites_row(70, 0, 3) Raster time raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :request_raster_irq(106, raster_bars_irq) :nops(14)
73. sprite_row_irq1: :exit_irq_handler() // Set the y-position, bitmaps and colors :sprites_row(70, 0, 3) Raster time raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :request_raster_irq(106, raster_bars_irq) :border(RED) :border(GRAY) :nops(14)
74. sprite_row_irq1: :exit_irq_handler() // Set the y-position, bitmaps and colors :sprites_row(70, 0, 3) Raster time raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :request_raster_irq(106, raster_bars_irq) :nops(14) :border(RED) :border(GRAY) :border(GRAY) :border(ORANGE)
75. sprite_row_irq1: :exit_irq_handler() // Set the y-position, bitmaps and colors :sprites_row(70, 0, 3) Raster time raster_bars_irq: :exit_irq_handler() // ... :request_raster_irq(60, sprite_row_irq1) :request_raster_irq(106, raster_bars_irq) :nops(7) :border(RED) :border(GRAY) :border(GRAY) :border(ORANGE)
77. More Sprites raster_bars_irq: :request_raster_irq( ) :exit_irq_handler() 60, sprite_row_irq1 sprite_row_irq1: // ... // ...
78. raster_bars_irq: :request_raster_irq( ) :exit_irq_handler() sprite_row_irq2: :border(CYAN) :sprites_row(160, 8, 12) :border(GRAY) :request_raster_irq( ) :exit_irq_handler() 60, sprite_row_irq1 sprite_row_irq1: // ... // ... More Sprites
79. raster_bars_irq: :request_raster_irq( ) :exit_irq_handler() sprite_row_irq2: :border(CYAN) :sprites_row(160, 8, 12) :border(GRAY) :request_raster_irq( ) :exit_irq_handler() 60, sprite_row_irq1 sprite_row_irq1: // ... // ... 150, sprite_row_irq2 More Sprites
81. Thin Green Line… :request_raster_irq(248, open_border_irq) open_border_irq: :border(GREEN) :nops(14) :border(GRAY) :request_raster_irq(60, sprite_row_irq1) :exit_irq_handler()
84. Opening the Border sprite_row_irq2: :request_raster_irq(248, open_border_irq) :exit_irq_handler() open_border_irq: :request_raster_irq(60, sprite_row_irq1) :exit_irq_handler()
85. sprite_row_irq2: :request_raster_irq(248, open_border_irq) :exit_irq_handler() open_border_irq: :request_raster_irq(60, sprite_row_irq1) :exit_irq_handler() // Enable 25 lines mode :set_bits(screen_control_register, %00001000) Opening the Border
86. sprite_row_irq2: :request_raster_irq(248, open_border_irq) :exit_irq_handler() open_border_irq: :request_raster_irq(60, sprite_row_irq1) :exit_irq_handler() // Enable 24 lines mode :clear_bits(screen_control_register, %00001000) // Enable 25 lines mode :set_bits(screen_control_register, %00001000) Opening the Border
88. Draw Under The Border lda #%10110101 sta border_pattern
91. Music
92. // Import music from a file .pc=$1000 music: .import binary "music.bin" Music
93. main: // initialize music jsr music // Import music from a file .pc=$1000 music: .import binary "music.bin" Music
94. main: // initialize music jsr music // Import music from a file .pc=$1000 music: .import binary "music.bin" play_music: :border(YELLOW) jsr $music + 3 :border(GRAY) :request_raster_irq(248, open_border_irq) :exit_irq_handler() Music
96. Try It Youself! h/p:/ /64bites.com/raster-shaders/ Don’t Let Old Computers Die